The present patent application relates to non-crystallizing N,N'-disubstituted N-(2-hydroxyalkyl)-ureas and to the use thereof as hydrolysis protection agents in plastics which contain ester groups.
N,N'-disubstituted N-(2-hydroxyalkyl)-ureas or -thioureas which are used as hydrolysis protection agents for plastics that contain ester groups are disclosed in DE-A 2,106,726. One disadvantage of the ureas or thioureas which are described in this German Patent is their crystallinity, which makes it difficult to admix these ureas in a homogeneous form with plastics containing ester groups and to stabilize such mixtures. These disclosed ureas therefore have to be melted before processing which constitutes an additional operating step. This additional operating step and the crystallinity of these hydrolysis protection agents adversely affect the economics of using the ureas or thioureas described in German Patent 2,106,726 to stabilize plastics which contain ester groups.
Another disadvantage of using the ureas or thioureas described in German Patent 2,106,726 is thermal cleavage due to overheating caused, e.g., by incorrect processing during attempts to liquefy them before they are admixed with the plastics containing ester groups, which liquefaction step is often carried out at considerably increased oven temperatures. Thermal cleavage results in the formation of volatile iso(thio)cyanates which constitute a physiological risk to the processing operator. Over-heating can also occur when these known ureas are used in systems in which curing is conducted at elevated temperatures, e.g., during the processing of thermoplastics using continuous screw devices or during the cure of cast elastomers.